Twitter's new app for the iPhone and the iPod Touch became a haven for porn videos as soon as it was launched last week, and that has raised questions about Apple's (AAPL) policy on allowing apps that show adult content.

Pornographic content quickly became prevalent throughout Vine, the Twitter-owned app that lets users upload six-second videos shortly after becoming available for the Apple devices last Thursday.

Despite the videos, the app has been allowed to remain in the Apple App Store. Critics are accusing the Cupertino tech giant of having a double standard, since it has banned other apps with adult content.

Twitter apologized for the accident and explained its policy on adult content, saying those types of videos violate the app's guidelines and are removed. Twitter also said users who post porn can also be banned from using the app.